This invention relates to foot prostheses in general, and specifically to a prosthetic foot adapted for use by persons who have undergone what is known in the art as a Symes amputation. This amputation severs the foot from the leg near the ankle region. Because the Symes patient's calf and shin functions as the patient's stump for prosthetic purposes, any prosthetic device utilized by the patient must either be relatively compact so as to be attachable below the point of amputation, or must be configured to accommodate the patient's shin and calf while attached thereto or higher up on the wearer's leg.
Prior art prostheses available to Symes patients typically include an artificial foot bonded or bolted onto the bottom end of a socket worn on the patient's stump. Examples of prior art Symes-type prostheses include U.S. Pat. No. 3,874,004 to May, which teaches an artificial ankle joint which can pivot in simulation of a natural ankle, and U.S. Pat. No. 4,225,982 to Cochrane, which teaches an elongated socket secured to a rubber-filled cavity of a slipper member.
Other prosthetic foot devices include U.S. Pat. No. 3,335,428 to Gajdos, which attempts to duplicate the skeletal and skin structure of a natural human foot, U.S. Pat. No. 2,075,583 to Lange, which incorporates a rubber form mounted in operative relationship with a rigid metallic core, and U.S. Pat. No. 4,645,509 to Poggi, which teaches a prosthetic foot incorporating a monolithic keel or beam of relatively massive proportions intended to react to the load of an amputee's body during walking, running, jumping, and the like and to release the resultant stored energy to create foot lift and thrust complementing the amputee's natural stride.
These and other prosthetic foot devices, however, have significant deficiencies; for example, the May '004 and the Cochrane '982 patents achieve relatively focused and limited stress response because of their structure and reliance on hardened rubber members for flexure. Moreover, the component parts of the prostheses are too heavy and too rigid, as in Lange, or are too massive and monolithic, as in Poggi, to respond properly to the nuances of stress-response gradients characteristic of the human foot.
Certain of these performance deficiencies are overcome in U.S. Pat. No. 4,547,913 for my invention relating to a "Composite Prosthetic Foot and Leg" and U.S. Pat. No. 4,822,363 for my invention relating to a "Modular Composite Prosthetic Foot and Leg". Also, my pending applications Serial Nos. 07/337,374 (now U.S. Pat. No. 5,181,932) and 07/293,824 (now U.S. Pat. No. 5,037,444) disclose prosthetic foot devices with similar preferred materials and methods of manufacture, and with corresponding benefits therefrom.
Each of my aforementioned inventions is characterized by lightweight, elongated structures incorporating polymer impregnation of superimposed reinforcing laminae maintained in the desired configuration. Such configurations and constructions provide the desirable characteristics of strength and flexibility in the prosthetic member, and achieve a simulation of the performance of natural feet which had previously not been attainable. Such prostheses may be provided in modular assemblies, whereby the particular performance characteristics of a given prosthesis may be adapted and readily adjusted to meet the needs and activity level of the individual patient.
None of my prior inventions, however, is readily utilized by Symes amputees, because of the various constraints set forth above. Among other things, my prior prosthetic inventions are not configured to accommodate affixation to a Symes-type stump, in that the prostheses are not compact enough to be attachable below the point of amputation, nor are they configured to accommodate the patient's shin and calf while attached thereto or higher up on the wearer's leg.